Interfitting metal and wooden parts particularly in gun making



W. W. HENRY July 11, 1961 INTERFITTING METAL AND WOODEN PARTS PARTICULARLY IN GUN MAKING Filed Nov. 4, 1957 /f/ INVENTOR.

man1-:fram LLLHETII (Xga/IL qi w ATMP/v5 Y United States Patent 2,991,548 INTERFII'ITNG METAL WOODEN PARTS PARTICULARLY IN GUN MAKING Woodrow W. Henry, Granby, Mass., assignor to Savage Arms Corporation, Chicopee Falls, Mass., a corporatron of Delaware I Y A FiledN0v. 4, 1957, Ser. No. 694,208

. 4 Claims. `(Cl. 29-424) Thepresent inventionrelates to the art of intertting wooden and metal parts and finds particular utility in the artofgunmaking l .n i i Y One of the most difficult tasks of intertting: wooden and metal parts is found in the manufacture of .a widely rusedftype offrie. In this rifle both the receiver and the stock are provided with a pair of tangs which are inter digitated in assembly.. Such assembly is conventionally a tedious operation requiring great skill in fitting (by filing, sanding, etc.) the matching surfaces of the pieces. It is obvious that, under practical manufacturing conditions, cracks will be found between the interdigitated parts and these cracks can be so unsightly as to require the parts to be r'reworked or rejected entirely. An even worse result is that the interdigitated tang portions may be mperfectly seated and make endwise contact at only one or.Y two localized points. Theoretically a four point l be in a rough nished stage.

fective parts represents a very substantial loss, particu- 3 i larly in terms of labor spent on the defective stock itself and on salvaging the metal parts for future use.

i One object ofthe present invention is to eliminate the need for manually and individually removing high and low spots to interit wooden and metal parts and to increase the speed.` and accuracy with which such parts may be interiitted.

Another object is to increase the speed and accuracy with which .gun stocks may be assembled.

A further object is to assure a fourpoint bearing between` interdigitated tangs of receivers and stocks thereby if notfeliminating stock breakage upon tiringof the guns. 1

' The invention will be found in various novel steps including forming the wooden part to the approximate shape of the metal part which is to be seated therein or thereon but in suchfa; fashion ythat a relatively small amount or layer of woodinterferes with the proper intertting of said parts. The metal part, heated to between 700 F. and 900 F., is then forceably joined to interlit the metal -part on'the prepared seat whereby the inter fering wood will be displaced and compacted.

The above mentioned temperature range is suiciently high to actuallycause ,charring-V or carbonization of the wood and therefore, especiallyin gun receivers, it is prefableto take the additionalstep of introducing a charretarding'agent on the Prepared seat prior to forcing the seated metal part thereon.

The above and other related objects and features of the invention will now be described in greater particularity with reference to the accompanying drawing and the novelty thereof distinctly pointed out in the appended claims.

In the drawngs- Y FIG. 1 is a perspective view, with certain portions ice broken away and in section, of an industrial electric oven which can be employed in heatingl metal receivers;

FIG. 2 is a perspective view, partly in section and on a greatly enlarged scale, of a receiver and gun stock aligned for interdigital intertting of tang portions;

' FIG. 3 is an elevation of a jig and xture suitable for forceably interlitting the illustrated stock and receiver of FIG. 2;

FIG. 4 is a section, on an enlarged scale, taken on line IV--IV in FIG. 3; and

FIG. 5 illustrates the relative degree of interference on a portionof the seat prepared on the gun stock with the matching portion of the receiver frame.

The following disclosure deals with the interltting of a stock and freceiver (frame portion only) of a well known type and while the inventive steps herein outlined `have particular novel features pertinent to such stocks and receivers it will be apparent that the utility of the invention'as awhole is not so limited and in fact may well be practiced outside the art of gun making.

Referring to FIG. 2, 10 indicates a receiver frame havringtaugs 12, While 14 depicts a gun stock having tangs 16 (see also FIG. 4). At this point note can be taken thatvthe tangs 12 are of unequal length with the lower tang being the longer, while the tangs 16 are of equal length; These proportions are well established by the functionaldesign of the gun and have nothing to do with the'present invention other than to illustrate one of the more diicult interfltting operations. Y

:It is preferable that, prior to intertting, the gun stock 'I'his means, among other things that its shape will approximate that of a finished stock but that all of its exterior dimensions will be oversize.l Of greater importance to the present invention the socket between the tangs 16, which serves as a seat for the tangs 12, yis formed undersize. In other words there is an interference of material which prevents a free intertting of the two parts. This condition is best illustrated in FIG. 5 where the shape of the socket between tangs 16 is seen in full lines and the seat required for the tang 12 isshown in dotted lines. The distances x represent the amount of this interference which may vary widely from a few thousandths to `as much as a of an inch or more in limited areas.

With this relative relation of the gun stock and receiver in mind, reference will next be had to the heating of the receiver.` While satisfactory results have been obtained lby heating the receiver to temperatures within the range of 700 to 900 F., a narrower range of 800 to 825 F. has been found preferable. One method of so heating the receivers is to place them in an electric furnace or oven 20 as indicated in FIG. 1. It has been found that if a group of receivers is left in the oven they will come upto hea in about 10 minutes. Preferably the oven heat is set for the higher limit of the above-mentioned preferred range, namely 825 F. so that when brought out for assembly the receiver will not cool below the desired' lower limit prior to completion of assembly.

It is convenient at this time to coat the seats of the wooden stocks with a char-retarding compound while waiting for the receivers to be heated. As has been brought out above the present invention involves displacement of Wooden libres by pressing the heated receiver against such seat. It can here be noted that the heats employed are sufficient to char or carbonize the wood but not high enough to ignite it. 'Ihese temperatures have been found necessary in order to displace the required amount of wood to give proper interitting of the parts with a of tolerance control of the sizes of such parts. While the use of a char-retarding compound is not vital in all cases, the size or mass of Patented AJuly 11, 1961 acceptable results are obtainedA only when a char-retarding compound s used. Otherwise uncontrolled chai-ring might result, a condition which would not only show up as a highly objectionable line 'of discoloration` on. the finished wooden piece adjacent the'contacting areas b-vf tween the parts but alsovcould detrimentally alect the physical properties of the wood. The use of a charretarding compound not only prevents objectionable dis-.- coloration but also the charred'wood which isV displaced retains substantially the same physical strength properties so that the resultant product is in -fact stronger. because of the equal distribution of forces due tothe uniform and complete surface contact between the two pieces.

The selection of a char-retarding compound isV based on the ability of the material to limit the spread of char and is believed to be the result of a blanketing effect which limits the availability of oxygen tothe wood as it is contacted by the heated receiver. Petroleum jelly has been found preferable not only in limiting or controlling char but also because it d oes not discolor the wood in any objectionable manner. However, otherv greases, jellies and the like could be employed particularly where discoloration is not of prime importance.

With the seat of the stock 14- coated with, petroleum jelly it is ready for assembly with the receiver Pref-i erably a jig such as is seen in FIG. 3 is used. This jig comprises a saddle 18 for receiving the stockl 14, when said saddle is in retracted position. 'I'he tangs 12` of the heated receiver may be first manually inserted and posi tioned between the tangs 16, due to the slight taper, as seen in FIG. 5, thereafter the stock is placed in the saddle 18 and the receiver 10 is placed in a fixture 201` in abutting relation to a cross piece 21. A clamp 22 may also be placed over the tangs 16 topreventV spreading when the parts are forceably brought together. r[he saddle 18 is next advanced along horizontal guide rods 2244 by rotay tion of a jack screw 25 which is threaded into a fixed upright 26 and provided with a handwheel 28 at its outer end. The parts are thus brought to the relative positions seen in FIG. 3 with the tangs 12 firmly seated betweenA the tangs 16 and with the ends of said tangs firmly seated against the stock and receiver respectively toprovide .the above-mentioned four point bearing which evenly distributes the impact forces involved in firing the gun. By way of further explanationof four point bearing, charrng and displacement of wood bres occurs most importantly at the ends of the two tangs 16 whichv are forced against lands, as at 30, on the receiver, and charring and displacement also occurs at the top and bottom of the socket between the tangs 16, as at 32 and 34-'('FIGS. 3 and 5).

In passing it will be observed that tongues 36 extend from the tangs 16 in a conventional fashion.' 'I'hese tongues are received by recesses in the receiver to prevent spread of the tangs 16 after assembly.

It will be appreciated that by using the above-described fixture a fair amount of force can be provided in seating the receiver. Experiments have shown that this force should be in the order of 500 to 1,000 pounds for the illustrated stock and receiver. However,v the amount of force will varyin relation to the size of parts and the amount of wood to be displaced'.

It has also been found that the preferred temperatures are so high and the mass of the receiver so great that the char-retarding effect yof the petroleum is only temporary in nature. ThisY is, if the assembled parts are left untouched, an objectionable charring of the wood is likely to, result. Twov possible solutions. toy this problem have been discovered. One is to disassemble the parts immediately after they have been properly seated. It has also been found that this disassembly should be done within 20 to 30 seconds after the parts have been firmly seated. Such disassembly Ythusr involves keeping thel stocks andreceivers` in matching pairs so that they may later be reassembled. For this reason the receiver i`s preferably cooled `by directing blast of coolingvairf or other cooling medium on the receiver immediately after proper assembly to prevent .undesirable-` and uncontrolled char- Y ring of the wood.

It will, of course, be appreciated.v that theeabove-described method could Vequally as Well be carried out'byf automatic means within the spirit and scope' of the present; invention; I y I 1 Having thusV described the invention, what is novel. and

' desired tov be patented' by Lenersv Patent Vefithe United forcing the said correspondingly shaped portionV againstsaid seat to form an intimate contact fit therebetween by displacing, compressing and charring thelinterfering-woodi portions, the charringv action being controlledy by the charretarding compound..

2. In the manufacture of firearms comprising a tangedil receiver interdigitatedl with! atanged stock; the steps. of

forming on each, seats. for receiving the tangs ofthe other, with an interference of wood on the stock preventing the tangs of eachfrom being fully interdigitated,. coating with a char-retarding compound the portions of the stock tangs which are to contact the receiver tangs,

heating the receiver to 700-900 F., interdigitating the stock tangs and receiver tangs and` seating the receiver tangs against the stock and the stock tangs against the. receiver to obtain a four point bearing between' thestock andi the receiverk by compressing and charting said interfering wooden portions of the ends of the stock tangsE and the seats of the stock against which the receiver tangs are seated to obtain full interdigitationofv the tangs: the charring action being controlled by'the char-retarding compound and cooling the receiver after obtaining saidY four point bearing.

3. The method Vof claimA 2 wherein petroleum jelly isused asthe char-retarding compound.

vl. The method of claim 3 wherein the the vstock is. formed with a seat 'for receiving the sides, as well as. the ends,A of the receiver tangs, saidv seat having an interference preventing -free interdigitationwith the receiver tangs,. the stock and receiver tangs are forcibly 'interdigitated and the stock tangs are prevented from spreading as-they` are interdigitated. f

References Cited in the file ofthisV patent l UNITED' STATES PATENTS Scott Ilme 1, 1954' 

